The present invention comprises a knife assembly for a chipping canter or similar small log sawmill device which may be readily and simply removed for sharpening or repair. The knife assembly is especially well adapted for use on chipping canters having a plurality of knife retaining segments mounted on a common shaft so as to define a generally cylindrical chipper head when in operation.
At the present time, approximately half of the sawlogs in the United States and Canada are processed through primary breakdown devices including a chipper as an integral part. These chippers create flat faces on one or more sides of the log to simplify downstream processing. The portions of the log that would formerly have been removed as slabs are thereby converted into salable pulp chips. Such devices are frequently called "canters" since the log is usually configured by the chippers so that it is converted into one or more cants of predetermined dimensions after subsequent primary sawing. A "cant" is a sawn or otherwise processed piece of wood of rectangular cross section intended for further processing into boards or dimension lumber.
The most popular chipping canters are configured to have a plurality of individual segments stacked one upon the other on a common shaft. Each segment normally has two replaceable peripheral cutter knives. Adjacent heads on a given shaft are normally rotated so that the cutter knives are displaced by 90.degree.. Knives are retained in notches on the periphery of the segment by a heavy dog or gib fastened with a single bolt.
One device using chippers of this type is sold as the Chip-N-Saw chipping canter/primary log breakdown unit. Chip-N-Saw is a registered trademark of Kockums Cancar, a Hawker Siddeley company of Vancouver, B.C.
The knives of a chipping canter of the type described above have a cutting edge approximately 50 mm in length and are made of a single piece of steel. The top to bottom dimension of these knives changes as they are ground for sharpening. In order to compensate for this, before replacement on the machine they are placed in a jig and a babbit shim is poured adjacent the base. In this manner a constant cutting radius can be maintained. In some positions on a typical installation, the knives are routinely replaced as frequently as every four hours. Depending on the maximum log size to be processed through the machinery, from 20 to 50 chipper segments employing twice this many knives are used. Knife replacement and maintenance forms a major item of operating expense. Before grinding for resharpening the babbit must be stripped from the base. A number of knives are placed side by side in a jig and shimmed or otherwise adjusted to bring the edges to a common height. Then a contoured grinding wheel traverses the knives to resharpen them. Each individual knife must then be removed and rebabbited before it can again be installed on the machine. The grinding wheels themselves represent a significant expense. Their life is relatively short since they must frequently be dressed to maintain a precise and complex edge configuration.
Others have in the past looked at chipping canters with an object of simplifying knife maintenance. One such effort is described in U.S. Pat. No. 3,356,114 to Noel. Here the knife is a simple arcuate or crescenticshaped blade which extends the full length of an elongated cylindrical chipper head. This blade is frictionally held in place in an arcuate seat on the chipper head by a dog-and-jib arrangement. Normally the base will be babbited or otherwise shimmed to ensure a constant cutting radius.
Other than the above arrangement, little attention appears to have been given for simplifying and reducing the cost of chipper blade maintenance. The technology that has long been available for installing replaceable teeth in circular saws appears not to have been adapable on a practical basis to chipper heads. In the most common arrangement for sawteeth, arcuate cutouts are made in the periphery of a sawplate. These cutouts, which are typically about 180.degree. to 270.degree. of a circle, are formed with a male V-shaped keel over most or all of their length. A crescentic-shaped locking segment having a corresponding V-groove is used in the arcuate cutout to hold a separate tooth in place. The following United States patents are representative of some of the earlier variations in this generic concept: Woodcock, U.S. Pat. No. 1,356,682; Brown, U.S. Pat No. 1,140,021; Freas, U.S. Pat. No. 1,831,705; and Charlton, U.S. Pat. No. 2,117,147. These and many subsequent similar patents are primarily directed to minor variations in tooth configuration to ensure tightness and stability during operation.
There has been a long felt need within the sawmilling industry for a chipping canter knife which would have longer life and could be more simply, economically, and rapidly maintained. These needs have now been filled by the knife assembly of the present invention.